1. Technical Field
This invention relates to technology for modifying the surface hardness of metal parts that have a near net-shape form, and more particularly to electrochemical techniques for achieving such hardness modification.
2. Discussion of the Prior Art
Selective surfaces of Ferrous based articles have been hardened by melting the surface with high energy, such as by electron bombardment, laser light, or plasma stream, and allowing the body of the Ferrous metal to chill the melted surface to produce a phase hardened surface. Metal surfaces have been hardened by thermal chemical treatment wherein molecules from an electrode or from a surrounding gas medium is impregnated into the metal surface. Surfaces have also been hardened by adhesion of superimposed films of harder material.
High energy beams are disadvantageous because they are difficult to regulate, expensive to operate and often require safety measures to protect the user. Thermal chemical treatments require a delicate and sophisticated energy producing apparatus in a tightly enclosed chamber which makes the system difficult to use and is expensive. Adherent layers of harder material often complicate and distort the near net-shape of the article so that it is more difficult to achieve an exact final shape of the article without increasing the cost of manufacturing.
Applicant is unaware of hardening of non-allotropic metals, such as aluminum, by electrochemical treatment wherein an electrical discharge across an insulative dielectric fluid causes globules of the non-allotropic metal surface to melt and upon removal of the electrical discharge, the globules are allowed to resolidify with alloying elements in the dielectric or metal surface forcing substitutional alloying and a harder surface. Applicant is aware of an electrochemical process, often referred to electrical discharge machining, that has been used to progressively remove surface metal from articles but with no attention to controlling hardness of the resulting work piece surface.